GaN-based light-emitting diode (LED) structures used in the production of high brightness light emitting diodes (LEDs) typically require removal of a sapphire or SiC substrate through laser lift-off (LLO) for transfer to conducting substrates. Such laser liftoff techniques are discussed in, for example, U.S. Pat. No. 6,071,795 and U.S. Pat. No. 6,420,242. This lift-off method is typically costly as high power lasers are used and large area sapphire/SiC substrates which are expensive are required. Also, a typical sapphire/SiC substrate is limited to a 6 inch wafer size and hence, growth potential to larger substrate sizes is limited. Also, use and maintenance of high power lasers is typically complicated and the lasers are difficult to control resulting in non-uniform yield from wafer to wafer during laser lift off of large diameter wafers. Furthermore, since sapphire substrates are insulators, for flip-chip LEDs, heat dissipation is a significant concern.
Growth of GaN on bulk Si or large area Si-based substrates is more cost effective and may lead to higher manufacturing yield. On the other hand, a significant concern for LEDs formed on Si substrates is the typical absorption of blue-green light emitted from the active layers of InGaN/GaN multi-quantum wells of the LEDs. Therefore, to obtain high brightness LEDs, removal of the Si substrates is typically necessary. In this regard, high brightness LEDs can be achieved by transferring LED structures grown on bulk silicon substrates to conducting substrates by wafer bonding or chemical lift-off processes. However, the internal quantum efficiency of LED material on bulk Si is typically lower due to a higher defect density. The defect density typically arise from a high lattice and thermal mismatch between silicon and GaN, leading to tensile stress, cracking and lowering of light emitting efficiency. Therefore, it is typically necessary to achieve high quality epitaxial LED structures on large area silicon platforms prior to fabrication of such high brightness LEDs.
Hence, in view of the above, there exists a need for a method for forming a light emitting diode structure and to a light emitting diode structure that seek to address at least one of the above problems.